WAH KIU YAT POT HALLO
三第四第
日五十月二十年午芮撰复
英文中
會考試題預習專欄
育敎僑華
化學科
(十三)
·王錦釗·
CHEMISTRY (13)
英文中學會考試題預習專欄
1. (a) The equivalent weight of an acid is the number of parts by weight of the pure acid which contains 1
part by weight of hydrogen replaceable by s metal. (b) A decinormal
solution of a compound is a solution containing one-tenth of one gram-equivalent of the compound in a litre of the solution.
H2SOL 1x 2 + 32
物理科
(十三)
梁海明
98 gms of H230
Weight of H-50
PHYSICS (13) B.M.Leung
Solution.
23.(a) Let x" be the wadth of
the rear window which the
man can see, From the
figure using similar tren angles we obtains.
18-20
In 20
Answer: The length of the rear window which the
man can see is 20 in.
(b)
98
*. 16 x
contain 2 gma. of replaceable. 82). containing 1 m of replaceable s
.98
2.
49. gna
49
$8230 + 2H20
Hence equivalent weight of H2SOL
H2SO
2NaOH
2NaOH
Na 250* 2n20
98 2(23+16+1) 982 x 40
Wt, of NaOH that reacts with 98 gms of 8,30,, - 2 x 40 gua
blusing the formule for mirrors
→
*
u
where u is the distance between the object and the pole of the mirror, v is the distance be-, tween the image and the pole of the mirror. f is the distance of the focus to the pole.
(c)
f. 10 cm.
སྐ
Lath be the height of the image,then
h
4
1.5
·
.". b1-20 cm
1
- - -15 Cn.
Or we use the graphical method as shown in the following diagrams
Wt. of NaOH that reacts with 49 gms of H2SO 40 gm
Hence equivalent weight of NaOH - 40
CaCO3 28C1 CaCl2
40+12+16x3· · ·2(1+35.5)
100
2 x 36.5
Equivalent wt. of HC1 - 36:
+.
Wt. of Caco, that reacts with 2 x 16.5.
- 100 gms
Wt. of CaCO, that reacts with 36.5 gms HC? 50 gms.
Hence equivalent weight of CaCO3 50
KHOO HCICI CO
+12+48 +35
100
Wts of KHCO3 that reacts with
valent at of KH
+2 naOH
98
2x40
4940
equivalent weight
230
HCI 100
「七千人一公年六十五國民解中
Three common alicators used in volumetric analysis :
-re lite, methyl orange and phenolphthalein.
The conditions under which each of these indicators Are used is as follows:
TITRATION
Strong acid - strong base
e.g. hydrochloric acio against caustic soda
2. Strong acid -weak base or carbonate
*.z. sulphuric acid against sodiu
carbonate
3. Weak acid - strong base -
*.g. bcetic acid against caustic soda
• Weak acid-weak base
e.g. acetic acid against ammonium!
hydroxide
INDICATOR
Litaue
methyl orange
phenolphthalein -
no indicator →→ is suitable
To determine the concentration in grams per litre of given solution of sedium carbonate. using a stand- ard solution of hydrochloric acid,
2/C1 + Na2003 2(1-35.5) 23x2+12*16x'
2x 36,5 =46+12+48
10t··
+++
2 NACI
CO, +
The equivalent weight of HCl = 36.5
-_- Na2CQ3 ** 106 +7a).
$3
Suppose the concentration of the given 'acid solution
W gms per litre.
Then the normality of the acid =
36
By titrating the acid against the carbonate solution, the normality of the carbonate solution may be calculated from the results, and hence the concentration in grams per litre may be obtained.
Procedure
By means of a 25 ml. pipette, transter exactly 250.0. of the sodium carbonate solution to a clean titrating. flask, and two drops of methyl orange are added.
2. The standard acid solution is then put into a burette. The acid is slowly and carefully run into the carbon- ate solution until the colour of the indicator changes
from yellow to orans
The volume of acid used is, then recorded
5. The titration is repeated several times, and the
volume of acid required for each titration is recorded. Calculation:
Let average volu
of acid required per titration
V.C.C.
25 ml. of Na, CO solution vc.c. of 15 N-HC1
The normality of Na2003 solution #
Scale: | in ± 10 CM
115 on 10 om
Scale in 10c
(111)
HaOH
Concentration of the NaOH solution: Normality
por litre
27.5 al of #
Normality of
lence the concentration of Na
solution
Ᏹ
Hence concentra
0: The strong ad
state
hence subst
and the
57 g/litre---10/
rabl
In pure solution.of hese
by disso)
ing in me. For ex
a solution of hydrogen entrations and is very
eld is hygroscopic some acid, it will be concentrated nitric acid concentrations and
le while coustic soda is del
STIONS FOR NEXT
be how you ould prepare and collect some, gas Jara
hydrogen
How could you show experimentally that hydrogen chloride fa contains hydrogen, (b) is very soluble in water ? Describe one experiment in each case with hydrochloric acid
(b), how Adsshaw (q) how it can act as a reducing agent,
may be ident ried.
Hydrogen chloride is soluble both in water and toluene,
do the properties of the solution in water differ from the solution in toluene? What arethe reasons for the diff-
in Lehaviour of the two solutions 7 State three ways in which hydrochloric acid resembles the other, common Laboratory mineral acids and three waya in Chich it differs from them
{(c) By calculationi
24.()
Answer The
4s erect virtual and 140 in".
behind the
Tough surface
If the direction of the refected light iss indepent of the direc- tion of the inciden light, it is called diffuse reflection. Diffuae reflection- always takes place at any rough surface.
The Law of Reflections
Polish surface. If all the reflected light goes in ons dir- ection, it is called. regular reflection. Regular reflection takes place at polisher surfaces
at the point of incidence and the reflected
((5)
same plane,
reflect fo) is equal to the angl,
Imag 18 Formed by he actual insectio) whereas a
parent
sal image is one formed ion of rays when their directions have been produced backwards. The practical distinction is that a real image ok. be formed on a screen while a virtual image cannot. We illustrate the difference by drawing ray diagrams of a concave, mirror.
(1) If the object le placed beyond the focal
distance
image 1e real.
(11) In the object is placed within the face)
distance
image 18
In the tag, ABU.
an incident ray - parallel to):
the principal ax
PC of a concave mirror"
ray, the normal to the mirror
By the law off Lecti and AB is parallel to CP.
Now B
ve
AFBC 18 i90sce fel
CF FB close to
we can take
PP
but
[FC CPX. FC FP
2FP r21
Topics for revision the ok.
Refraction of light at a plane surface, angle of Incidence and of refraction, refractive index Snell's Law. Real and apparent depths
Total interual reflection, critical angle
Questions .
(25:(a)) (Véfine refractive inder, citical angle and
deduce the relation between them.
(b) a parallel beam of light falls on the surfaos water at an angle of incidence or 60° and je partly reflected, partly refracted. Assuming tha refractive index of water to be 4/3, find, by calculation or by diagram, the directions of the reflected and refracted rays,
5) An equilateral glass priem stands on a horizon-
tal surface and a horizontal ray of light strikęs. one face at ite middle point, By construction show the path of the ray through the prism and measure the total deviation. The refractive index of the glzas - 3/2 A small fist object,
a coin, lies at the. bottom of a tank containing water to a depth of 16 on. Find the apparent position of the coj when viewed from directly above. Does the
object appear to be the same size as it doe when the tank is empty? Give reasons.
26.)
A transparent cube of 15 cm, edge contains, a small air bubble. Its apparent depth when viewed through the o опа
face, it is 6 on.
and when viewed through the opposite face it 14 4 cm. Find the actual distance of the bub- ble from the first face, and the refractive": inder of the substance of the
cube. (0) Explain, with the aid of a diagram, how, a suitable glass prism may be used to turn ray of light through 180
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